It is known that polyethylene terephthalate (PET) now constitutes the plastic material of choice for producing containers for drinks due to the fact that it does not release potentially toxic substances into the contents.
It is also known that current regulations do not allow the abovementioned containers to be reused.
Therefore large quantities of disposable PET containers are being accumulated.
In this description and the subsequent claims, the PET of the aforementioned disposable containers is indicated by the terra "recycled PET".
The Italian Patent Application No. M191 A 002949 filed on Nov. 6, 1991 pointed out the uneconomical nature of the methods proposed to date for disposing of the abovementioned containers (incineration or depolymerisation and recovery of the monomers) and proposed recycling polyethylene terephthalate (PET) by extruding it into shaped sheets for building.
In particular, the abovementioned application proposed washing PET containers, crushing them and drying them thoroughly up to a moisture content of from 20 to 50 ppm. The resulting material was then crystallized, mixed with an inert mineral filler and extruded in flat sheets finally, the latter could be shaped in the form of corrugated sheets or other profiles, for example fretted, by conventional machines and techniques,
The shaped sheets obtained in this way were however found to be highly crystallized, with poor elasticity and low impact strength, a sheet with thickness of 3 mm breaking on the impact of a cylindrical striking mass, with spherical head and weighing 2 kg, from a height of only 0.2 m.
The Japanese Patent Application Opened No. 92,536/83 describes a biaxially-oriented plastic bottle comprising a bottom portion, a body portion, a shoulder portion and a neck portion formed by biaxially-oriented blow molding a parison of virgin polyethylene terephthalate, wherein said neck portion has a highly crystallized outer surface layer with density of no less than 1.36 g/cc, and a less crystallized inner surface layer with density of no more than 1.35 g/cc.
In order to achieve such crystallization the outer surface of the neck portion is heated at 180.degree. C. for 30 seconds to 1 minute white the inner neck portion is maintained at a lower temperature.
However, when this procedure was utilized to manufacture a shaped sheet made from a blend of recycled PET and an inert mineral filler, unsatisfactory results were obtained (see Comparative Example 1).